This invention relates to a system for protecting structures, e.g., buildings, bridges and machines such as printing presses, from the effects of seismic disturbances and, more particularly, to a pendular, friction-based system affording improved damping of seismic disturbance forces.
With reference to FIG. 1 herein, U.S. Pat. No. 4,860,507 of the present inventor (hereinafter "the '507 patent") discloses a stabilization system 10 for protecting a structure 12, e.g., a building, from effects of seismic disturbances. The stabilization system 10 includes a base isolation system 14 employing vertical support columns 15, suspended by flexible elements from corresponding bases 16. This system 14 provides "floating" support of the structure 12 relative to its foundation 18, thereby minimizing horizontal movement transmission from the ground, during a seismic event, to the structure 12. A releasable interlock system 20 and a damping subsystem 22 are employable independently of, and/or in combination with, this base isolation system 14. More particularly, the releasable interlock system 20 normally secures the structure 12 to its foundation 18 against linear displacements below a predetermined threshold level. The system 20, however, has an automatic release mechanism responding to forces above the threshold, as may be produced by a seismic disturbance. These forces automatically unlock the structure 12 and permit same to "float", supported by the base isolation system 14.
The damping subsystem 22, on the other hand, employs hydraulically interconnected hydraulic dampers 24, 26, arranged as one or more pairs. Each pair contributes to providing suitable damping of linear relative displacement between the structure 12 and its foundation 18. These dampers, it has been found, may help create, due to their arrangement, a tendency for the structure to gyrate about a vertical axis relative to its foundation, but also serve to impede this gyration, once created.
U.S. Patent No. 5,152,110 of the present inventor (hereinafter "the '110 patent") further discloses an improved damping subsystem employing hydraulic dampers of "L-shaped" configuration which provide a hydraulic parallel-to-perpendicular force, or displacement, transformation. Each L-shaped damper has first and second integral, angularly related damper components. Remote subchambers of the damper components are hydraulically connected via a valved conduit, and adjacent subchambers are directly connected hydraulically. The valve is adjustable, to produce a desired level of damping.
The disclosures of the '507 and '110 patents are expressly incorporated herein by reference and effectively as though each was directly incorporated herein in its entirety.
In the present inventor's U.S Pat. No. 5,797,277, there is described a base isolation system including a support frame assemblage of a plurality of vertical support columns arranged in a pair of parallel (longitudinal) rows and secured to the earth (e.g., by pilings). The respective vertical support columns of the parallel rows are disposed in paired, spaced relationship; longitudinal support beams interconnect the respective columns of each row, and transverse (or lateral) support beams extend between and interconnect the paired columns of the parallel rows.
A support slab having parallel longitudinal edges is disposed in spaced, parallel relation between the parallel rows of vertical support columns and the associated, longitudinally extending support beams, so as to extend in parallel therewith in the longitudinal direction. Elongated pendulum arms, e.g., solid core steel rods, are engaged at upper ends thereof to upper portions of the vertical support columns and at lower ends thereof to the slab, affording a pendulum-type suspension of the slab from the vertical support columns. This arrangement is analogous to the pendulum-type "floating" suspension of the building as taught by the '507 patent. Furthermore, a hydraulic damping system using orifice plugs interconnects the slab to the supporting foundation to which the vertical support columns are connected.
The rods have knuckle joints including a hemispherical, convex knuckle element functioning as a dry bearing surface in frictional engagement within a corresponding concave socket. The rods have threaded ends which are inserted through supports and receive nuts thereon. Adjustment of a nut adjusts the length of the rod.
The knuckle element is movable within its corresponding socket, so that the slab may float relatively to, and thereby be isolated from, the support columns and related support structures which are subject to movement during seismic disturbances. This frictional engagement is described in U.S. Pat. No. 5,797,227 as supplementing the damping effects of the hydraulic damping system, but only after a small displacement of the slab relatively to the vertical support columns and thus relative gyration of the rod ends, or knuckles, within the corresponding sockets defining the bearings, i.e. after such relative displacement or movement overcomes an initial dynamic friction at the bearings.
There remains a continuing need for improvements in such systems to enhance the effectiveness of same and to broaden the range of applications in which they may be employed, while simplifying the implementation of same as well. For example, it is highly desirable to provide a structure stabilization system for protecting machinery, such as a printing press, from seismic disturbances, where the printing press is to be installed and operated in a pre-existing building which has no, or inadequate, seismic protection; it is also desirable to protect such equipment without having to significantly modify the building or any existing base isolation system, both as a matter of convenience and to assure that a unitary, or integral, support structure is afforded.
It is also desired that a potential relative gyration between the building and foundation not be created, due to the character of a base isolation system, in the event of a seismic disturbance. More particularly, as noted above, as hydraulic dampers may actually contribute to the creation of forces tending to gyrate the building relatively to its foundation, a damping system which does not rely upon such hydraulic dampers is also desired.
Eliminating a hydraulic damper-based system could also lead to a less complex, less expensive, lower maintenance and higher dependability system for protecting a structure from seismic disturbances.
It is also desired to have a relatively simple device for isolating a structure, such as a bridge deck, from seismic disturbances experienced by the bridge's piers. For optimum efficiency and performance, such device should be capable of use in new construction or in retrofitting an existing bridge, should be adjustable to compensate for ground settling, should be maintenance free, and should not contribute to torsional forces which might tend to gyrate the bridge deck.